As Traveller 2 said it all depends on how you plan on using it. If your going to "Snowbird" then better than normal isulation would be nice, but if your staying in a cold climate then I'd go for the heavy insulation package. With that said however we have been out in 13 degree weather with a standard FW and MH and had no issues, of course we didn't have that temp for a prolonged period of time. The one we just ordered has an "arctic package" since we may do more stays in the colder climates,
As to the generator, I think it is much better having it installed at the factory, They know how it's supposed to fit and I doubt you would save much money having it installed later.